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Discovery of 245 Hz burst oscillations from the accreting millisecond pulsar IGR J17511-3057

ATel #2199; A. L.Watts (U. v. Amsterdam), D. Altamirano (U. v. Amsterdam), C. B.Markwardt (U. Maryland & NASA/GSFC), T. E.Strohmayer (NASA/GSFC).
on 15 Sep 2009; 13:43 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Diego Altamirano (diego@science.uva.nl)

Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 2215, 2216, 2220, 2232, 2506, 2529

RXTE observations of the bursting accreting millisecond X-ray pulsar IGR J17511-3057 (ATEL #2196, #2197, #2198) showed a short Type I X-ray burst on September 14th 2009. We detect strong burst oscillations at 245 Hz, very close to the spin frequency. Maximum Leahy power is in the range 130-215 in 3 independent consecutive 4s bins during the burst (using all photons in the 2-60 keV band), putting the detection beyond doubt. Burst oscillation amplitude exceeds 10% rms in this energy band.

There is no strong evolution in burst oscillation frequency during the burst. This is very similar behaviour to that of the burst oscillations from the accreting millisecond pulsar XTE J1814-338 (Watts, Strohmayer & Markwardt 2005).

Note that we have verified that we are not simply detecting the accretion-powered pulsations during the burst: the amplitudes are such, and the countrates in the peak of the burst sufficiently high compared to the persistent emission, that the burst emission itself must be pulsed.